This disclosure relates generally to medical diagnostic instruments, such as ophthalmoscopes and otoscopes. For example, a number of known instrument designs, such as those manufactured by Welch Allyn Inc., of Skaneateles Falls, N.Y., are detailed in U.S. Pat. Nos. 6,106,457, 7,029,439, 7,399,275, and 7,670,287, each of which are incorporated herein by reference in their entirety.
Otoscopes can include a port that enables caregivers, such as clinicians, to insufflate the ear of a patient in order to provide a more complete diagnostic examination. An example of a known pneumatic otoscope 400 is partially depicted in FIG. 11, including an instrument head 404 that includes an attachment end 408 that is securable to a handle (not shown). The instrument head 404 is defined by a hollow interior and includes a distal end that retains a distal insertion portion 410 (partially shown) that is shaped and configured to support a speculum tip element 412, the latter being insertable to a predetermined distance within the ear canal (not shown) of a patient. At the opposing rear or proximal end of the instrument head 404, a viewing lens 416 is pivotally attached to the instrument head 404 at an upper end via a connection 424, the viewing lens 416 including a lens tab 428 extending from a lower or bottom end. The viewing lens 416 forms a seal with the interior of the instrument head 404 wherein the viewing lens 416 can also include a peripheral bumper 418. A insufflation port 420 extends into the interior of the instrument head 404 wherein a pneumatic bulb (not shown) and hose (not shown) can be fluidically connected to the insufflation port 420. Squeezing the pneumatic bulb enables air under pressure to be directed to the ear of the patient.
Successful pneumatic otoscopy requires a sealed innerformer. A typical innerformer is disposed within the interior of the instrument head and serves to support the distal insertion portion and further enables optical fibers from a contained illumination assembly to be directed to the exterior of the distal insertion portion. Leaks developed in the instrument can prevent adequate pressurization. Without proper pressurization, the ear drum will not deflect as intended and the user may thus misdiagnose fluid behind the ear when in fact it does not exist. In the case of some leaks, the user may hear air hissing from the device and try to compensate with ever more vigorous hand pumping. These quick blasts do not allow adequate pressure modulation and in fact can injure the delicate ear drum.
Prior art otoscopes tend to suffer from leaks, either at the time of manufacturing or after a period of use. Leaks occur for many reasons, but among the most common is a poor seal between an interface defined between the viewing lens at the proximal end of the instrument head and the mating innerformer surface. This interface has a large perimeter that presents many opportunities for air to escape the instrument. If either the viewing lens or the innerformer deviates from flat surface to surface contact, an air passage can result along at least a portion of the periphery of the lens and the innerformer. One possible solution would be to manufacture these parts with extremely high tolerances. This solution would drastically increase the overall cost of the assembly and also increase the number of components that would have to be discarded in order to meet the higher tolerance thresholds. Still further, nicks, scratches or other manufacturing defect on either surface (the rear of the innerformer assembly and the interior periphery of the lens) would produce the same deleterious effect. While these problems may not exist at the time of manufacture, even with high tolerance manufacture, these problems could easily result over time and use of the instrument based subjecting the instrument to shock or impact loads (e.g., drops), the usual sliding motion of the lens relative to the innerformer to effect instrumentation, and other use case scenarios.
More specifically, a drop may produce gross deflection of the innerformer within the instrument head, thereby moving the rear surface relative to the interior peripheral contacting lens surface. This dynamic motion of one component relative to the other can scratch or otherwise damage the sealing surfaces. Otoscopic instruments that do not protect the innerformer from impact forces are especially vulnerable to this latter issue.
The above noted sealing interface between the lens and the rear surface of the innerformer may also leak if the lens retention means of the instrument applies inadequate or unbalanced forces to the lens. Insufficient restraining forces allow air pressure to push the lens away from the innerformer. As a result, airleaks are produced from the resulting gap. Similarly, an unbalanced restraining force may tip the lens such that one peripheral section lifts off or away in relation to the sealing interface. As a result, the section that is lifted away also becomes prone to undesired air leakage. This latter situation can arise at the time of manufacturing due to tolerance variations, but this undesired situation may also occur because the various components warp or otherwise migrate or creep over time and changes in environmental exposure.
Other than creating a higher degree of tolerancing, an alternative technique applied in some prior art otoscopes to effectuate a proper seal is the addition of an elastomeric sealing member disposed at the above-defined interface. While employing an elastomeric seal can provide an airtight junction, this proposed solution requires the added expense of the elastomeric component, as well as other parts or features that become necessary in order to constrain the elastomeric part. Elastomeric parts can also tear or wear away (erode) when the pivoting lens repeatably slides over them in use. Further, elastomeric compounds used in the manufacture of sealing members (e.g., O-rings) can degrade with time and temperature or exhibit a residual adhesion effect (i.e., ‘stiction’), whereby the elastomeric components adhere to the lens over time and rip away or are otherwise rendered unsuitable for providing an adequate air seal with the interior of the instrument head when the user finally slides the lens